Headsets are often employed for a variety of purposes, such as to provide bi-directional voice communications for human-to-human or human-machine interaction. These interactions can take place in a voice-directed or voice-assisted work environment, for example. Such environments often use speech recognition technology to facilitate work, allowing workers to keep their hands and eyes free to perform tasks while maintaining communication with a voice-directed portable computer device or larger system. A headset for such applications typically includes a microphone positioned to pick up the voice of the wearer, and one or more speakers—or earphones—positioned near the wearer's ears so that the wearer may hear audio associated with the headset usage. Headsets may be coupled to a mobile or portable communication device—or terminal—that provides a link with other mobile devices or a centralized system, allowing the user to maintain communications while they move about freely.
Headsets typically include a multi-conductor cable terminated by an audio plug, which allows the headset to be easily connected to and disconnected from the terminal by inserting or removing the audio plug from a matching audio socket. Standard audio plugs are typically comprised of a sectioned conductive cylinder, with each section electrically isolated from the other sections so that the plug provides multiple axially adjacent contacts. The end section is commonly referred to as a “tip”, while the section farthest from the tip is referred to as a “sleeve”. Additional sections located between the tip and the sleeve are known as “ring” sections. An audio plug having three contacts is commonly referred to as a TRS (Tip Ring Sleeve) plug or jack. Standard audio plugs are also commonly available with two contacts (Tip Sleeve, or TS) and four contacts (Tip Ring Ring Sleeve, or TRRS), although other numbers of contacts are sometimes used. Standard diameters for TRS type plugs include 6.35 mm, 3.5 mm, and 2.5 mm, and the connectors also typically have standard lengths and ring placements so that different headsets may be used interchangeably with a variety of terminals.
As communications systems have evolved, one trend has been to add active electronics to headsets to improve their performance and increase their functionality. Headsets today may include active noise reduction and signal enhancement circuits that process signals from multiple microphones, as well as other signal processing or conditioning circuits and devices, such as microphone biasing circuits and audio amplifiers. As more functionality is added to headsets, the associated electronic circuitry creates a need for power. One way of providing power to a headset is with a battery or similar power storage device located in the headset. However, batteries undesirably increase the size and weight of the headset, and must be regularly replaced or recharged, adding to the cost and maintenance burden of operating a powered headset. The cost and maintenance burdens are particularly undesirable in a work environment, since the headset may stop functioning unexpectedly when the battery exhausts its charge, potentially stopping work until a replacement battery or headset can be provided.
To avoid placing a battery in the headset, it has been proposed that power may be supplied to the headset from the terminal into which the headset is plugged. For example, additional conductors and connector contacts could be added to the terminal/headset interface to allow power to be directly sourced from the terminal. However, doing so would require changes in both headset and terminal hardware, and would create additional compatibility issues with standard multi-contact TRS type connectors. For this reason, headsets and terminals having the additional conductors might not be sufficiently compatible with older equipment to provide even original levels of functionality, thus increasing the total number of terminals and headsets which must be purchased, maintained, and tracked. In addition, as the number of separate conductors increases, the size and cost of cables and connectors also undesirably increase.
Another method that has been proposed to provide power to the headset is to allow power and audio signals to share a single conductor by multiplexing out of band power signals, such as a DC signal or high frequency carrier, with existing audio signals. One such method is described in U.S. Patent Application Pub. No. 2012/0321097, entitled “Headset Signal Multiplexing System and Method”, filed on Jun. 14, 2011, the disclosure of which is incorporated herein by reference in its entirety. However, multiplexing power signals and audio signals onto the same conductor has other drawbacks. For example, such multiplexing increases the peak composite signal voltage levels, which can cause clipping and distortion in the limited amplitude channels characteristic of most terminal audio input/output circuits. Therefore, to allow audio and power signals to share the same limited amplitude channel, often either the power level of the baseband audio signal will need to be reduced, impacting the ability of the headset to provide sufficient audio volume to the wearer, or the amplitude of the carrier will need to be reduced, impacting the amount of power that can be delivered to the headset.
Yet another method that has been proposed to allow sharing of a limited amplitude channel that avoids the power sharing problems associated with audio and power signal multiplexing is to use a carrier signal employing constant envelope modulation, such as frequency modulation. In this type of system, power is provided to the headset by the constant envelope carrier, with the audio information modulating the carrier's frequency or phase. However, because the constant envelope carrier approach requires the audio signals to be recovered by an appropriate demodulation process on the receiving side, it is incompatible with existing headsets, and thus undesirable for at least all of the aforementioned reasons associated with methods requiring incompatible connectors.
Therefore, there is a need for improved methods and systems for providing power to headsets, and in particular, for coupling power from terminals to headsets over existing standard connector and cable interfaces in a way that is compatible with existing terminals and headsets.